Electric valve converting system



July 1, R TRQGER ETAL ELECTRIC VALVE CONVERTING SYSTEM Filed June 21, 1959 2 Sheets-Sheet l lrwventors FQichard Trger, Otto Qenner,

b UM

Then" Attorney.

July 1, 1941. R TRO ET AL 2,247,793

ELECTRIC VALVE CONVERTING SYSTEM Filed June 21, 1959 2 Sheets-Sheet 2 Fig.3.

Inventors: Qicl'ward Trc'jger,

Otto Qenner, by W a Them Attohnegl Patented July 1, 194-1 UNETE YATES n rcpt-1 ATNT (LE ELECTREC VALVE CONVERTING SYSTEM Application June 21, 1939, Serial No. 28%,336 in Germany July 29, 1938 Our invention relates to electric valve converting systems and particularly to such systems wherein a plurality of serially connected electric discharge valves are utilized.

For very high voltage installations where electric valve converting systems are used, it has sometimes been found desirable to operate a plu rality of electric valves in series whereby at least two important advantages are obtained. in the first place, each individual discharge valve need not be designed to withstand the full voltage of the system, and in the second place, much greater reliability of o eration is obtained for in the present state of development of commercial electric discharge valves one cannot be sure that the individual valves will never fail. However, by using a number of electric discharge valves in series the probability of failure of the system can be greatly reduced. Furthermore, even though any one electric ischarge valve should fail the strain on the remaining serially connected valves would be increased only by a small amount and the probability of failure of the remaining valves would be very remote. When such valves are connected in series and employed in high voltage installations, there exists the danger that the voltages, and especially the inverse voltages, will not be uniformly distributed among the various valves and a large proportion of the inverse voltage may appear across one of the valves causing it to flash over. If, however, some means were provided for causing the various valves to assume equal proportions of the voltages irnpressed upon them, this diiiiculty would be eliminated. It has been suggested in such arrangements that the secondary winding of the electric valve converting apparatus transformer be subdivided into a number of individual windings and that each of the serially connected electric discharge valves be joined to one of these subdivided windings so that the total voltage is uniformly graded and positively distributed among the various serially connected discharge valves. However, since electric discharge valves sometimes fail or are back even at normal voltages impressed upon them, it is necessary to provide some means to maintain the increase in current which occurs when one of the serially connected valves arcs back within safe limits. Specially designed transformers have been used which afford a high reactance in case of abnormal current conditions but these transformers are both difficult and expensive to construct, and furthermore can only be operated within a very definite range. Accordingly, we provide an arrangement wherein a normal transformer be used in connection with the electric valve converting apparatus and yet wherein are back currents are kept within safe limits.

It is an object of our invention to overcome the disadvantages above noted in connection with electric valve converting apparatus employing serially connected discharge valves.

It is another object of our invention to provide a new and improved electric valve converting system.

It is a further object of our invention to provide a new and improved electric valve converting system of the type wherein a plurality of serially connested electric discharge valves are used.

In accordance with the illustrated embodiment of our invention, we provide an arrangement for limiting the arc back current in an electric valve converting apparatus for transmitting energy be tween a polyphase alternating current circuit a direct current circuit through a plurality of groups of serially connected electric discharge valves, one group of serially connected valves for each phase of the alternating current supply circuit. Uniform distribution of voltage among the serially connected valves is positively obtained by means of a subdivided secondary transformer winding having one of the subdivisions connected between each of the serially connected valves. A plurality of inductive windings are provided for limiting the are back current in any of the valves which windings offer a very high impedance to arc back currents and yet offer a very limited or negligible impedance to the normal low of current through the electric valve converting apparatus.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, will best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a diagrammatic representation of an electric valve converting apparatus employing a plurality of of serially connected valves to which our invention has been applied; Fig. 2 is a modification of the embodiment illustrated in Fig. l, and Fig. 3 is a modification oi the arrangement illustrated in Fig. 2.

Referrin now to Fig. l of the drawings, we have illustrated therein an electric valve converting apparatus for transmitting energy be tween an alternating current circuit in and a direct current circuit ll. lthough our invention is applicable to any of the electric valve converting systems well known in the art in which a plurality of serially connected electric discharge valves are utilized whether converting from alternating to direct current, or vice versa, for simplicity in disclosure and explanation we have illustrated an arrangement wherein three-phase alternating current is converted into direct current.

As illustrated, a transformer [2 has its threephase Y-connected primary phase windings l3, l3 and i3" energized from the alternating current source l9. These windings are wound on a suitable three phase core symbolically shown as M. On each of the legs of core M of transformer l2 are wound the secondary phase windings which are subdivided into a ntunber of steps for each phase. The subdivisions of the secondary winding associated with primary phase winding l3 are designated by the numerals l5, i6, i1 and it, while correspondingly those associated with primary phase winding 53 ii and I8 and those associated with primary phase winding l3 are designated by numerals l5", IS, [1 and I8". Aphuality of electric discharge valves I9, 2B, 21 and 22 are connected between each step of the subdivided secondary windings 15, IE, 11 and 13, respectively, while the electric discharge valves is, 29, 2| and 22, it, 2e", 2! and 22" are connected, respectively, between each step of the subdivided secondary windings !5', H5, I1, l8, l5, I6", I? and I8. Electric discharge valves 19 to 22" may be may of the electric discharge valves well known to those skilled in the art, although our invention is particularly applicable for use with the type of valves wherein a plurality of electrodes are mounted within an envelope containing an ionized medium. Accordingly, we have shown each of the electric discharge valves H to 22", respectively, as comprising an anode 23, a cathode 24, and a control electrode or grid 25. The cathodes of the electric discharge valves 22, 22 and 22 are connected through a suitable smoothing reactor 26 to one side of the direct current circuit l l, while the other side of the direct current circuit H is connected to one terminal of each of the subdivided secondary windings l5, l5 and iii". In order to maintain the are back current within safe limits in case one of the electric discharge valves should fail we provide inductive windings 21, 28, 29, 30-3051, 21, r

3', 29, SW-Eda, 21", 28", 29", 3Q30a", connected in series with the cathodes of each of the valves 9 to 22", respectively. Each of the inductive windings 21 to 23 comprises a plurality of coils 3! and 32 reversely wound upon a suitable core 33. A normal flow of current through the coils 3! and 32 in series will produce zero resultant ampere turns and hence there will be zero resultant flux in core 33. Thus inductive windings 21 to 29 will offer a very low impedance to normal current flow through the serially connected electric discharge valves 18 to 22; I9 to 22' and I9 to 22". In connection with the last electric discharge valves in the series connected groups for example, discharge valve 22, there is provided a coil 3| wound on core 33 which is inductively related, by means oi windings 3i and 35a connected in a series circuit, with reversely wound coil 32 thus operating in the same manner as inductive windings 21, 28, etc. Similarly inductive windings 3030a and 3B"la" comprise reversely wound coils 3! and 32 inductively related by means of windings 34'-34a' and 34"34a", respectively.

The operation of the electric valve converting are designated as l5,

system may briefly be described as follows: An alternating potential derived from the polyphase source ill is applied to the primary phase windings l3, l3 and 3" of transformer l2 and correspondingly to the subdivided secondary phases !5, l5, l1, l3, l5, l6, l1, l8, l5", l5", l1 and 8". The phase embodying the particular group of serially connected discharge valves l5 to 22, to 22 or IE" to 22 upon the anodes of which the highest positive potential relative to the cathode is impressed at any instant will be conductive as is well understood by those skilled in the art. Let us assume, for example, that current is flowing through electric discharge valves I9, 20, 2i and 22, through smoothing reactor 25 to the direct current circuit l! and returns from the other side of the direct current circuit H to the anode 23 of electric discharge valve l9 through coil 32 and subdivision I5 of the secondary winding of transformer l2. It will be observed that this current flows through the reversely wound coils 3i and 32 of each of the inductive windings 21, 23, 29 and 3il-30a connected in series with the respective discharge valves 19, 20, 2| and 22. Since the resultant or net ampere turns of inductive windings 21 to SQ-tfia are zero the impedance offered to the current flowing through these windings during normal operation is negligible. When the positive potential applied to the next group of serially connected valves I9, 2O, 21, 22 becomes equal to or higher than the potential applied to the serially connected valves 19, 20, 2 l, 22 which have just been conducting current, commutation of current between the groups of valves will occur and valves H3, 2| and 22 begin to conduct current. If now an are back should occur, for example, in electric discharge valve I9 current will tend to flow through coil 3| of inductive winding 2?, through coil 3| oi inductive winding 21 and through electric discharge valve 18 in the reverse direction. Since a corresponding current does not flow through coils 32 of inductive windings 21 and 21 their ampere turns are no longer neutralized and the net resultant flux induced in the cores 33 is no longer zero. It follows, therefore, that a high impedance is offered by coils 3| of inductive windings 21 and 21 to the arc back current thus maintaining it Within safe limits. The coils 3| of inductive windings 21 and 21 thus become effective chokes to limit the arc back current and yet afiord little or no impedance to the normal operating current. It will of course be understood that inductive windings 21, 28, 29 and 30-3!Ja instead of being wound on four individual cores symbolically shown as 33, may all be wound on one single phase core. Also, it would be possible that each of the inductive windings 21, 21' and 21" be wound on a three-phase core instead of three single phase cores 33 as illustrated in Fig. 1, since the midpoints of inductive windings 21, 21' and 21" are all interconnected by means of conductor 35. Hence, a plurality of three-phase cores embody ing the inductive windings 21, 21, 21"; 23, 28, 28"; 29, 23, and 30a, 3933a, 30" 39a" may be connected between the corresponding discharge valves of all of the phases. The arrangement may be still further simplified by placing all the inductive windings 21, 21, 21", 28 3U36a" on a common three-phase core as will be understood by those skilled in the art.

From the operation just described of the apparatus illustrated in Fig. 1 when an are back occurs in discharge valve it, it will be observed that due to the inductive coupling of coils 3| and 32 a voltage may be induced in coil 32 of both windings 2i and 2'! when are back current flows in coils 3i and 3! of the inductive windings. This voltage induced in coils 32 of inductive windings 2'! and 2? will cause a. voltage to e impressed on electric discharge valves 29 and 29 without affecting the voltage impressed on the remaining electric discharge valves 2|, 22 and 2|, 22 of the respective serially connected groups. This additional voltage may cause an are back in electric di charge valve 2%, for example, whereas if this voltage due to arc back current were divided equally among the remaining valves no additional are back would occur. Hence it would be desirable to have a uniform distri bution of this voltage among the remaining dis charge valves so that the probability of rc back in the remaining electric discharge valves becomes more remote. This result is obtained by the arrangements disclosed in Figs. 2 and 3.

In Fig. the corresponding circuit arrangements are characterized by the same reference numerals as in Fig. 1. For simplicity in disclo sure, however, only three serially connected electric discharge paths for each phase have been shown as contrasted with the four illustrated in Fig. 1. Alternating current from alternating current supply circuit it is converted to direct current supplied to direct current circuit H by means of the electric valve converting apparatus embodying transformer 32 and a plurality of serially connected discharge valves Iii, 2B, 2!; i8, 2s, Eli; and l3", 2%", 2i", respec tively for each phase of the polyphase alternat ing supply circuit ill similar to the arrangement disclosed in Fig. 1. In order to maintain the are back current within safe limits in case one of the electric valves should fail we provide inductive windings comprising transformers 35, 3b, 36", 3?, ill, 3?" and 3t, 35", one winding of which is connected in series with each of the cathodes 2 t of electric discharge valves 59 to 2|, respectively. The other windings of transformers 36, 3'1 and 35 are connected in series in a closed circuit 39. In a similar manner the other windings of transformers 36', 5-3? and 33' are connected in series in a closed circuit 43 and the other windings of transformers 8G", 3'! and 38" are connected in series in a closed circuit 4|. During the normal operation of the electric valve converting apparatus illustrated in Fig. 2 the plurality of transformers 35 to 33" afford little or no impedance to the normal currents flowing through the serially connected electric discharge valves since the impedance aiforded by these transformers is the same as that of a transformer with a short circuited secondary winding. If, however, an are back occurs in one of the electric discharge paths, for example in electric discharge valve it, then a reverse current will tend to iiow through the winding of trans former 35 connected in series with the cathode 24 of elect *ic discharge valve l8. Assuming for example, that at the instant an are back occurs in valve l9 electric discharge valves I9, 257 and 2 i are conductive then the reverse current flowing through the winding of transformer 3b in series with cathode 24 of electric discharge valve ill will induce a current in the other winding of translormer 3's which is connected in closed circuit 3%! in series with corresponding windings of transformers 31 and 33. However, since no current is flowing at this time through electric discharge valves 20 and 2|, the windings of transformers 31 and 38 which are in series with these valves are effectively open circuited and hence these transformers afford a very high impedance to any current flowing in circuit 39 and furthermore transformer 36 affords a very high impedance to the are back current thus maintaining it within safe limits. The advantage of this arrangement over that disclosed in Fig. 1 resides in the fact that whenever an are back occurs the current which is caused to flow in closed circuits 39, Ail or 4|, depending upon the particular valve which arcs back, will cause the additional potential created by virt e of the are back current to be divided equally among the remaining valves in the particular serially connected group of valves containing the valve which has failed, and hence an equal distribution of the voltage will be obtained as contrasted with Fig. 1 wherein all the voltage will appear on the next adjacent series connected discharge valve.

Although in Fig. 2 we have illustrated the in ductive windings comprising transformers 35 to 38 as connected in series with the cathodes of electric discharge valves l9 to 2|", it will be understood that these inductive windings could equally well be connected in series with the anodes of the respective discharge valves. This latter arrangement has the advantage that electric discharge valves comprising a plurality of anodes may then be used instead of a single electric discharge valve for each serially connected discharge path. Accordingly, in Fig. 3 we have shown inductive windings comprising transformers 3E, 35, 3G, 37, 31, 3?", 38, 38, it, connected in series with the respective anodes of the various discharge paths. Also, instead of separate discharge valves is, 29, and |9" we have shown a single discharge valve 42 comprising a plurality of anodes and a single cathode 2 Likewise electric discharge valves 2Q, 25) and 2d of Fig. 2 have been shown as a single discharge valve 43 in Fig. 3 and discharge valves 2|, 2|, 2| have been shown as a single discharge valve 44 in Fig. 3. The operation of the electric valve converting apparatus illustrated in Fig. 3 is of course identical with that ascribed in connection with Fig. 2 and will be well understood by those skilled in the art.

While we have shown and described particular embodiments of our invention as applied to an electric valve converting apparatus, it is to be understood that this is merely illustrative as one of a number of electric valve converting or translating apparatus to which our invention may be applied. It will, of course, be obvious to those skilled in the art that changes and modifications may be made without departing from our invention and we, therefore, aim in the appended claims to cover all such changes and modifica tions as fall Within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for transmitting energy between direct and alternating current circuits comprising a plurality of electric discharge valves connected in series relation, means for impressing an electromotive force upon said valves, electric translating apparatus connected in parallel with each of said discharge valves, and .a plurality of inductive windings, connected between successive ones and in series relation with each of said electric discharge valves for limiting the are back current due to the failure of any valve.

2. In combination, a polyphase alternating current circuit, a direct current circuit, means for transmitting energy between said circuits comprising a plurality of electric discharge valves arranged in groups according to the number of phases of said polyphase alternating current cir cuit, the valves of each group being connected in series relation, means comprising a plurality of inductive windings effectively connected in series with the valves of each group and offering a low impedance to load current flowing in a normally conducting group of valves while offering a large impedance to current flow resulting from any of the valves in the other groups becoming conductive in a reverse direction.

3. In an electric valve convertin system, the combination of a plurality of serially connected electric discharge valves, means for impressing an electromotive force upon said valves, and means including an inductive winding comprising a pair of reversely wound coils connected in series with said valves for limiting the are back current due to the failure of any valve.

4, Apparatus for transmitting energy between direct and alternating current circuits comprising a plurality of electric discharge valves connected in series relation, means for impressing an electrcmotive force upon said valves, and a plurality of transformers each having one of their windings connected in the anode circuit of one of said serially connected valves while the other windings are connected in series in a closed circuit with all the corresponding windings of said transformers associated with those valves connected in series relation.

5. In combination, a polyphase alternating current circuit, a direct current circuit, means for transmitting energy between said circuits comprising a plurality of electric discharge valves arranged in groups according to the number of phases of said polyphase alternating current circuit, the valves of each group being connected in series relation, means comprising a plurality of transformers one winding of each transformer being connected in series with the cathode of each of said electric discharge valves while the other winding of said transformer is connected in series with the corresponding windings of the remaining transformers associated with one of said groups of electric discharge valves for limiting the current when any one of said plurality of valves becomes conductive in the reverse direction.

6. In combination, a polyphase alternating cur rent circuit, a direct current circuit, means for transmitting energy between said circuits comprising a plurality of electric discharge valves ar ranged in groups according to the number of phases of said polyphase alternating current circuit, the valves of each group being connected in series relation, means comprising a plurality of transformers one winding of each transformer being connected in series with the anode of each of said electric discharge valves while the other winding of said transformer is connected in series with the corresponding windings of the remaining transformers associated wtih one of said groups of electric discharge valves for limiting the current when any of said plurality of valves becomes conductive in the reverse direction.

7. In combination, a polyphase alternating current circuit, a direct current circuit, means for transmitting energy between said circuits comprising a plurality of electric discharge valves and a main transformer, said plurality of electric discharge valves adapted to be serially connected in groups according to the number of phases of said polyphase alternating current circuit, said main transformer having a primary Winding connected to said polyphase alterating current circuit and a secondary winding provided with a plurality of subdivisions according to the number of electric discharge valves arranged in each of said groups, the valves of each group boing connected in series relation with the subdivisions of the secondary winding of said transformer in order to positively insure equal distribution of potential on all the electric discharge valves connected in series, and means comprising a plurality of inductive windings for limiting the current when any of said plurality of valves becomes conductive in the reverse di rection.

8. In combination, a polyphase alternating current circuit, a direct current circuit, means for transmitting energy between said circuits comprising a plurality of electric discharge valves arranged in groups according to the number of phases of said polyphase alternating current circuit, the valves of each group being connected in series relation, means for limiting the are back current due to the failure of any valve including an inductive winding comprising a pair of reversely wound coils connected in series with the valves of each group, said reversely wound coils having a common terminal, and means for completing an electrical circuit between the common terminal of the reversely wound coils associated with one of said groups of valves with the common terminal of the reversely wound coils associated with each of the other groups of valves.

RICHARD TRCGER.

OTTO REN'NER. 

